The present invention relates to a system for detecting trouble of an intake system of an automotive engine.
A fuel injection system in which a basic fuel injection quantity is determined in accordance with pressure in an intake pipe and speed of the engine is used for automobiles. In such a system, if a trouble of the intake pipe occurs, such as the coming out of a blind cap on the intake system downstream of a throttle valve which is caused by backfiring, air is induced in the intake pipe passing through a hole for the blind cap without passing the throttle valve. The pressure in the intake pipe rises with the induced air. As a result, the fuel injection system operates to increase the basic fuel injection quantity in accordance with the high intake pipe pressure, which causes an abnormal increase of the speed of the engine regardless of driver's intention.
Japanese Pat. application Laid-Open 58-214632 discloses a system for solving such a problem. The system stores reference data of intake pipe pressure determined by the opening degree of the throttle valve and the engine speed. Detected intake pipe pressure is compared with a stored reference pressure. If the detected pressure is higher than the reference pressure, the basic fuel injection quantity is fixed to a predetermined value, thereby preventing an abnormal increase of the engine speed.
However, at an engine transient state, such as when a depressed accelerator pedal is quickly released, although the reference pressure immediately decreases as a result in the large decreases of throttle opening degree and engine speed, the actual pressure slowly decreases because of the capacity of the intake passage. Consequently, as shown in FIG. 4, the actual pressure becomes higher than the reference pressure, so that abnormality in the intake system is erroneously determined.